Apparatus for receiver equalization

ABSTRACT

In some embodiments an apparatus includes an amplifier, a first inverter having an input coupled to an output of the amplifier, and a second inverter having an input coupled to an output of the first inverter and an output, where the output of the second inverter is fed back to an input of the amplifier. Other embodiments are described and claimed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/607,799, filed Jun. 27, 2003 now U.S. Pat No. 7,227,414.

TECHNICAL FIELD

The inventions generally relate to receiver equalization.

BACKGROUND

Conventional wide band amplifiers such as CMOS (Complementary MetalOxide Semiconductor) amplifiers have a difference in gain between lowand high frequencies. This causes a condition referred to asinter-symbol interference (ISI), which causes a frequency dependentloss. Traditional receiver equalization schemes using analog or DSP(Digital Signal Processing) techniques are very complex, use a largenumber of transistors, and consume a large amount of power.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventions will be understood more fully from the detaileddescription given below and from the accompanying drawings of someembodiments of the inventions which, however, should not be taken tolimit the inventions to the specific embodiments described, but are forexplanation and understanding only.

FIG. 1 is a block diagram representation of some embodiments of theinventions.

FIG. 2 is a block diagram representation of some embodiments of theinventions.

FIG. 3 is a waveform diagram illustrating a problem that may be overcomeaccording to some embodiments of the inventions.

FIG. 4 is a waveform diagram illustrating some embodiments of theinventions.

FIG. 5 is a circuit diagram representation of some embodiments of theinventions.

FIG. 6 is a circuit diagram representation of an amplifier according tosome embodiments of the inventions.

FIG. 7 is a circuit diagram representation of an amplifier according tosome embodiments of the inventions.

FIG. 8 is a circuit diagram representation of an amplifier according tosome embodiments of the inventions.

FIG. 9 is a circuit diagram representation of some embodiments of theinventions.

FIG. 10 is a block diagram representation of some embodiments of theinventions.

DETAILED DESCRIPTION

Some embodiments of the inventions relate to receiver equalization. Someembodiments are implemented in any very high speed serial differentiallink receiver. Some embodiments relate to high speed serial differentialfrequency equalization.

Frequency dependent loss is inherent in CMOS (Complementary Metal OxideSemiconductor) circuits and in transmission lines. In some embodiments afrequency dependent loss created by inter-symbol interference (ISI) iscounteracted and compensated for. When a receiver must process a widefrequency spectrum of data the ISI may be removed using feedbackaccording to some embodiments. In some embodiments delay and/or gain areused to help remove the ISI. In some embodiments an amplifier is usedthat can realize the full gain bandwidth product potential of thetransistors that form the amplifier. In some embodiments this amplifieris an amplifier formed of CMOS (Complementary Metal Oxide Semiconductor)transistors. In some embodiments any self-biased amplifier or latch maybe used. In some embodiments a circuit is used that makes improvementsin high frequency performance for any given CMOS gate geometry to whichit is applied. In some embodiments the a circuit is used that makesimprovements and advancements in power efficiency and design simplicitywhile counteracting and compensating for the frequency dependent losscreated by ISI.

In some embodiments two inverters (for example, CMOS inverters) arecoupled in series to an output of an amplifier (for example, a selfbiased amplifier). The two inverters create a correct state to providenegative feedback to the amplifier. The circuit including the twoinverters provides delay and gain to the feedback. In some embodimentsthe closed loop gain of the amplifier never exceeds the open loop gainof the amplifier. In some embodiments the delay and gain are used toselect the frequency at which the maximum amplifier gain is achieved.

In some embodiments negative feedback is mixed at the self-bias controlof the amplifier. In some embodiments a hybrid of a Bazes amplifier anda Chappell amplifier is used. In some embodiments any self-biasingamplifier or latch is used. In some embodiments the amplifier uses aform of positive feedback to assist the amplifier gain. In someembodiments when positive and negative feedback signals mix, theirindividual effects are negated.

In some embodiments the longer the amplifier remains in one state, thecloser the positive and negative feedback signals approach the rails,the control voltage (for example, self-bias control voltage) approacheshalf supply, and the amplifier reduces to a minimum output level butdoes not change state. This arrangement is the opposite of one artifactof transmission line inter-symbol interference which tends to encouragesignals of long duration.

In some embodiments the negative feedback travels through two additionalinverters of propagation delay than the positive feedback. This meansthat for a period of time equivalent to the propagation delay the twofeedbacks (negative and positive) are pulling in the same direction. Thesystem momentarily provides the maximum amount of positive feedback tothe differential dV/dT on the input signal. This improves both theamplitude and width of the transition. This is the opposite of the otherartifact associated with inter-symbol interference which tends to resistsignals of short duration and leads to inaccurate output values in thosecases.

In some embodiments an amplifier is sized for best open loop bandwidth.In some embodiments a first inverter is one-fourth the size of theamplifier output to maintain loading as low as possible. In someembodiments the first inverter is one-fourth the size of the secondinverter in order to deliberately slow state propagation time throughthe negative feedback loop and minimize the possibility of the firstinverter creating another pole in the system.

In some embodiments the amplifier works on a differential dV/dT, energyin the transition, rather than an actual eye opening (or “I opening”) orcrossing. This allows the amplifier to extract correct information forma closed eye (or “closed I”).

In some embodiments positive feedback is applied to cross-coupled loads(e.g., using a p-channel amplifier, an n-channel amplifier and/or a CMOSamplifier). In some embodiments positive feedback is applied to improveperformance, and delay and gain is added. In some embodiments negativefeedback is applied.

In some embodiments an apparatus includes an amplifier, a first inverterhaving an input coupled to an output of the amplifier, and a secondinverter having an input coupled to an output of the first inverter andan output, where the output of the second inverter is fed back to aninput of the amplifier.

In some embodiments an apparatus includes an amplifier and a delay andgain circuit coupled to an output of the amplifier, where an output ofthe delay and gain circuit is fed back to the amplifier.

In some embodiments an amplifier includes an input, an inverse input, anoutput, a first p-channel MOSFET (Metal Oxide Semiconductor Field EffectTransistor) (pMOS transistor), a second pMOS transistor, a third pMOStransistor, a first n-channel MOSFET (nMOS transistor), a second nMOStransistor and a third nMOS transistor. The first pMOS transistor has agate coupled to the input of the amplifier. The third pMOS transistorhas a gate coupled to the inverse input of the amplifier and a sourcecoupled to a source of the first pMOS transistor and to a drain of thesecond pMOS transistor. The first nMOS transistor has a gate coupled tothe input of the amplifier. The second nMOS transistor has a gatecoupled to a drain of the first pMOS transistor, a drain of the firstnMOS transistor, and to a gate of the second pMOS transistor. The thirdnMOS transistor has a gate coupled to the inverse input of theamplifier, a drain coupled to a drain of the third pMOS transistor and asource coupled to a source of the first nMOS transistor and to a drainof the second nMOS transistor. The output of the amplifier is coupled tothe drain of the third pMOS transistor and to the drain of the thirdnMOS transistor.

In some embodiments a system includes a transmitter, a receiver, and atransmission line (or interconnect) coupled to the transmitter and thereceiver. The receiver includes an amplifier and a delay and gaincircuit coupled to an output of the amplifier, where an output of thedelay and gain circuit is fed back to the amplifier.

In some embodiments a method includes providing delay and gain to anoutput of an amplifier, and feeding back an output from the delay andgain to the amplifier.

In some embodiments a method includes amplifying an input signal, andcompensating for a frequency dependent loss by feeding back an outputsignal to the amplifying.

In some embodiments positive feedback and delayed negative feedback areapplied to an amplifier. In some embodiments gain is applied to delayednegative feedback that is applied to an amplifier. In some embodimentspositive feedback and negative feedback are mixed. In some embodiments aratio of positive feedback to negative feedback is balanced through gainon the negative feedback. In some embodiments positive feedback andnegative feedback are supplied in a proportion that compensates forand/or counteracts a frequency dependent loss created by inter-symbolinterference (ISI). In some embodiments positive feedback is appliedquickly and negative feedback is delayed (and/or applied slowly). Insome embodiments positive feedback and negative feedback are mixed toprovide a desired affect of compensating for inter-symbol interference(ISI). In some embodiments positive feedback is created by an amplifierand negative feedback is applied to the amplifier from a delay and gaincircuit. In some embodiments a delay and gain circuit includes twoinverters connected in series.

FIG. 1 illustrates an apparatus 100 according to some embodiments.Apparatus 100 includes an amplifier 102, a delay and gain circuit 104,and a feedback loop 106. Amplifier 102 may also be referred to in someembodiments as “the first stage”. Amplifier 102 may be a CMOS amplifierin some embodiments. Amplifier 102 includes two inputs, “in” and “!in”,where “!in” is the inverse signal from “in”. Delay and gain circuit 104has an input coupled to an output of amplifier 102. Delay and gaincircuit 104 has an output provided as an output signal. The output ofdelay and gain circuit 104 is also fed into feedback loop 106 to beprovided as a control input to amplifier 102. In some embodimentsfeedback loop 106 may include known feedback circuitry. In someembodiments feedback loop 106 provides the output of delay and gaincircuit 104 directly to the control input of amplifier 102.

FIG. 2 illustrates an apparatus 200 according to some embodiments.Apparatus 200 includes an amplifier 202, a first inverter 204, a secondinverter 206, and a feedback loop 208. Amplifier 202 may also bereferred to in some embodiments as “the first stage”. Amplifier 202 maybe a CMOS amplifier in some embodiments. Amplifier 202 includes an inputsignal “in” and an inverse input signal “!in”. First inverter 204 has aninput coupled to an output of amplifier 202. Second inverter 206 has aninput coupled to an output of first inverter 204. An output of secondinverter 206 is provided as an output signal, and is also fed into afeedback loop 208 as a control input to amplifier 202.

In some embodiments sizes of first inverter 204 and second inverter 206are used so that appropriate delay and gain are provided to the circuit.In some embodiments values of the inverters are chosen such thatnegative feedback is delayed as long as the smallest data change (thatis, duty cycle distortion) where some data has a small duration. In someembodiments the values of the inverters are chosen so that negativefeedback is delayed for a period corresponding to the period of thesmallest data bit frequency.

FIG. 3 illustrates signal waveforms 300 illustrating a problem that maybe overcome according to some embodiments. The waveforms 300 illustratedin FIG. 3 include an input signal waveform 302, an inverse input signalwaveform 304, and an output signal waveform 306. The illustrated inputsignal waveform 302, inverse input signal waveform 304 and output signalwaveform 306 occur, for example, with an amplifier arrangement that doesnot solve an inter-symbol interference problem solved by someembodiments. Input signal 302 exhibits a pattern with the followinglogic values: “11000001010011111010”. Inverse input signal 304 exhibitsa pattern with the following logic values: “00111110101100000101”.Output signal 306 initially drops to a low signal value (logic “0”) inresponse to the first two input signal 302 logic values “11” and inresponse to the first two inverse input signal 304 logic values “00”.Output signal 306 then rises to a high signal value (logic “1”) inresponse to the next five input signal 302 logic values “00000” and inresponse to the next five inverse input signal 304 logic values “11111”.Then when the input signal 302 rises to logic value “1” and the inverseinput signal 304 drops to logic value “0” the output signal 306 beginsto decrease. However, before output signal 306 is able to drop to alogic “0” value the input signal 302 drops to a logic value “0” and theinverse input signal 304 rises to a logic value “1”. This causes theoutput signal 306 to increase before it ever reaches a logic value “0”.This is a problem that can occur, for example, when the value of theinput has been at one logic value for a long time and then transitionsto the other value and back in a short amount of time. The output neverrecognizes the short transition value (in this case, output signal 306never registers a logic value of “0” in response to the short transitionof the input signal to a logic value of “1”).

A similar problem occurs after the input signal 302 stays at a logicvalue of “1” for a while. For example, when input signal 302 exhibits alogic value of “11111” and inverse input signal 304 exhibits a logicvalue of “00000” and then input signal 302 switches to a logic value of“0” and inverse input signal 304 switches to a logic value of “1” for ashort time period before switching back again a similar problem occursas illustrated in FIG. 3. The output signal 306 stays at a logic valueof “0” while the input signal 302 stays at a logic value of “1” for fivetime periods and while the inverse input signal 304 stays at a logicvalue of “0” for five time periods. However, when input signal 302switches to a logic value of “0” and inverse input signal 304 switchesto a logic value of “1” for one time period and then switches back againthe output signal 306 does not rise to a logic value of “1” beforedecreasing in response to the switch of the input signal back to “1” andthe switch of the inverse input signal back to “0”.

FIG. 4 illustrates signal waveforms 400 according to some embodiments.The waveforms 400 illustrated in FIG. 4 include an input signal waveform402, an inverse input signal waveform 404, and an output signal waveform406. The illustrated input signal waveform 402, inverse input signalwaveform 404 and output signal waveform 406 occur, for example, with anapparatus according to some embodiments.

Input signal 402 exhibits a pattern with the following logic values:“11000001010011111010”. Inverse input signal 404 exhibits a pattern withthe following logic values: “00111110101100000101”. Similarly to outputsignal 306, output signal 406 initially drops to a low signal value(logic “0”) in response to the first two input signal 402 logic values“11” and in response to the first two inverse input signal 404 logicvalues “00”. However, output signal 406 does not remain at the lowestanalog level as long as output signal 306 illustrated in FIG. 3. Outputsignal 406 begins to rise in value earlier than output signal 306,although it remains at a logic “0” value. Output signal 406 then risesto a high signal value (logic “1”) in response to the next five inputsignal 402 logic values “00000” and in response to the next five inverseinput signal 404 logic values “11111”. Although output signal 406 staysat a high logic value during the five input signal 402 logic values“00000” and five inverse input signal 404 logic values “11111” it doesdecrease in level during those five signal time periods. Then when theinput signal 402 rises to logic value “1” and the inverse input signal404 drops to logic value “0” the output signal 406 is able to decreasedown to a logic value “0” before the input signal changes again anddrops to a logic value “0” and before the inverse input signal changesagain and rises to a logic value “1”. In this manner, unlike the outputsignal 306 in FIG. 3 and according to some embodiments the output signal406 is able to recognize the transition that occurs after the value ofthe input has been at one logic value for a long time and then changesto the other value and back in a short amount of time.

Similarly, when input signal 402 exhibits a logic value of “11111” andinverse input signal 404 exhibits a logic value of “00000” and theninput signal 402 switches to a logic value of “0” and inverse inputsignal 404 switches to a logic value of “1” for a short period of timebefore switching back again the problem associated with output signal306 of FIG. 3 can also be avoided. The output signal 406 stays at alogic value of “0” while the input signal 402 stays at a logic value of“1” for five time periods and while the inverse input signal stays at alogic value of “0” for five time periods. However, unlike output signal306 in FIG. 3, output signal 406 does not stay at the same low voltagelevel. The voltage level of output signal 406 begins to rise in voltageduring the five time periods, but stays at a low (“0”) logic value. Wheninput signal 402 then switches to a logic value of “1” for one timeperiod and then switches back again the output signal 406 is able torise to a logic value of “1” before decreasing in response to the switchof the input signal back to “1” and the switch of the inverse inputsignal back to “0”.

FIG. 5 illustrates an apparatus 500 according to some embodiments. Insome embodiments apparatus 500 includes a p-channel MOSFET (Metal OxideSemiconductor Field Effect Transistor) (pMOS transistor) 502, ann-channel MOSFET (nMOS transistor) 504, pMOS transistor 506, nMOStransistor 508, pMOS transistor 510, nMOS transistor 512, resistor 514,resistor 516, pMOS transistor 522, nMOS transistor 524, pMOS transistor526 and nMOS transistor 528.

Transistors 502, 504, 506, 508, 510 and 512 (and in some embodimentsalso resistor 514) may form an amplifier according to some embodiments,which may be in some embodiments a wide band CMOS amplifier. Transistors522 and 524 may form a first inverter. Transistors 526 and 528 may forma second inverter. An output of the second inverter is an output of theapparatus 500. The output of the amplifier (also referred to as thefirst stage amplifier) has analog precharge artifacts. In someembodiments the analog precharge artifacts are similar to the saggingaffect illustrated in and described in reference to FIG. 3. The firstand second inverters (sometimes referred to as the second stage)restores digital level signaling so that no sagging affect is present atthe output of apparatus 500.

In some embodiments the amplifier in FIG. 5 may be used in otherembodiments such as the amplifier 102 in FIG. 1, the amplifier 202 inFIG. 2, the amplifier 1012 in FIG. 10, or other amplifiers. In someembodiments the first inverter in FIG. 5 may be used in otherembodiments such as the inverter 204 in FIG. 2, or may be included inother circuitry such as delay and gain circuit 104 of FIG. 1 or delayand gain circuit 914 of FIG. 9, or any other delay and gain circuit. Insome embodiments the second inverter in FIG. 5 may be used in otherembodiments such as the inverter 206 in FIG. 2, or may be included inother circuitry such as delay and gain circuit 104 of FIG. 1 or delayand gain circuit 1014 of FIG. 10, or any other delay and gain circuit.In some embodiments the first and second inverters in FIG. 5 may becombined to form circuits such as delay and gain circuit 104 of FIG. 1or delay and gain circuit 914 of FIG. 9, for example.

A gate of pMOS transistor 502 is coupled to the input “in”. A gate ofnMOS transistor 504 is also coupled to input “in”. A source oftransistor 502 is coupled to a drain of pMOS transistor 506 and to asource of pMOS transistor 510. A drain of transistor 502 is coupled to afirst terminal of resistor 514 and to a drain of nMOS transistor 504. Asource of nMOS transistor 504 is coupled to a drain of nMOS transistor508 and to a source of nMOS transistor 512. A gate of pMOS transistor506 is coupled to a second terminal of resistor 514 and to a gate ofnMOS transistor 508. A source of pMOS transistor 506 is coupled to ahigh voltage value V. A source of nMOS transistor 508 is coupled to aground voltage (and/or a low voltage value), a source of nMOS transistor524 and a source of nMOS transistor 528. A gate of pMOS transistor 510and a gate of nMOS transistor 512 are coupled to an inverse input “!in”.A drain of pMOS transistor 510 and a drain of nMOS transistor 512 areeach coupled to a gate of pMOS transistor 522 and a gate of nMOStransistor 524. A source of pMOS transistor 522 is coupled to the highvoltage value V. A source of nMOS transistor 524 is coupled to theground and/or low voltage value. A drain of pMOS transistor 522 and adrain of nMOS transistor 524 are each coupled to a gate of pMOStransistor 526 and a gate of nMOS transistor 528. A source of pMOStransistor 526 is coupled to the high voltage value V. A source of nMOStransistor 528 is coupled to the ground and/or low voltage value. Adrain of pMOS transistor 526 and a drain of nMOS transistor 528 arecoupled together and provided as an output signal “out”. This outputsignal “out” is also fed back through the resistor 516 to the gate ofnMOS transistor 508.

In some embodiments a resistor array of two or more resistors such asresistor 514 and 516 are used to mix a positive feedback applied to theamplifier by the amplifier itself with a negative feedback applied tothe amplfier from the output of the second inverter (at the output“out”). In some embodiments the resistors of the resistor array areconnected in series with each other. In some embodiments resistors 514and 516 passively mix the positive feedback and the negative feedback.In some embodiments resistors 514 and 516 are a passive mixing resistorarray connected in series with each other, where resistor 514 isconnected to positive feedback and resistor 516 is connected to negativefeedback and a mixed signal is provided at a connection point betweenthe two resistors. In some embodiments the positive feedback is appliedto the amplifier quickly and the negative feedback is applied to theamplfier more slowly due to the delay created by the two inverters. Thegain supplied by the two inverters may be used to provide a proportionalamount of negative feedback proportional to the positive feedback suchthat a frequency dependent loss and/or an intersymbol interference (ISI)is counteracted and compensated for.

The circuit illustrated in FIG. 5 can be used to solve the problemillustrated in FIG. 3 in a manner similar to that illustrated in FIG. 4so that, for example, a frequency dependent loss created by inter-symbolinterference (ISI) is counteracted and compensated for.

While FIG. 5 illustrates some embodiments using CMOS (ComplementaryMetal Oxide Semiconductor) implementations it is understood that otherembodiments may not use all MOS or CMOS technology, or any MOS or CMOStechnology.

In some embodiments the CMOS transistors of FIG. 5 may have a length of80 nm or of approximately 80 nm. In some embodiments widths of p-channeltransistors 502, 506, 510 and 526 are 9.2 um or are approximately 9.2um. In some embodiments a width of p-channel transistor 522 is 2.3 um oris approximately 2.3 um. In some embodiments widths of n-channeltransistors 504, 508, 512 and 528 are 4 um or are approximately 4 um. Insome embodiments a width of n-channel transistor 524 is 1 um or isapproximately 1 um. In some embodiments a resistance of resistors 514and 516 is 5000 ohms or is approximately 5000 ohms. In some embodimentshigh voltage value for the provided high voltage at the sources oftransistors 506, 522 and 526 are 1.2 volts or are approximately 1.2volts. Although exemplary values for transistor lengths, transistorwidths, resistances and provided voltages are provided above, othervalues for some or all of these elements may be used according to someembodiments.

The amplifier illustrated in FIG. 5 formed by transistors 502, 504, 506,508, 510 and 512 (and in some embodiments also resistor 514) may beviewed as a hybrid of a Bazes amplifier and a Chappell amplifier. Someembodiments use this hybrid amplifier. Some embodiments use a Bazesamplifier. Some embodiments use a Chappell amplifier.

FIG. 6 illustrates an amplifier 600 according to some embodiments.Amplifier 600 may be viewed as a hybrid of a Bazes amplifier and aChappell amplifier. Amplifier 600 is similar to the amplifierillustrated in FIG. 5. Amplifier 600 includes an input (“in”), aninverse input (“!in”), an output (“out”), a pMOS transistor 602, an nMOStransistor 604, a pMOS transistor 606, an nMOS transistor 608, a pMOStransistor 610, an nMOS transistor 612 and a resistor 614. In someembodiments resistor 614 could have any resistance, including zeroresistance (in such an embodiment there would be no resistor 614 and thelines coupled to the two terminals of resistor 614 would be directlycoupled together). The amplifier 600 illustrated in FIG. 6 does not needto include resistor 614. However, resistor 614 has been included to showthat the amplifier 600 may include a resistor 614 that is similar toresistor 514 illustrated in FIG. 5. In some embodiments resistor 614 maybe included in a resistor array or in a group of resistors in seriesthat are used to mix a positive feedback and a negative feedback similarto the resistors 514 and 516 in FIG. 5. In some embodiments resistor 614is included in a resistor array or a group of resistors connected inseries to passively mix a positive feedback and a negative feedback.

Each transistor 602, 604, 606, 608, 610 and 612 includes a source, adrain, and a gate. Resistor 614 includes a first terminal and a secondterminal.

The source of pMOS transistor 602 is coupled to the drain of pMOStransistor 606 and to the source of pMOS transistor 610. The drain ofpMOS transistor 602 is coupled to the first terminal of resistor 614 andto the drain of nMOS transistor 604. The gate of pMOS transistor 602 iscoupled to the input “in” and to the gate of nMOS transistor 604.

The source of nMOS transistor 604 is coupled to the drain of nMOStransistor 608 and to the source of nMOS transistor 612. The drain ofnMOS transistor 604 is coupled to the first terminal of resistor 614 andto the drain of pMOS transistor 602. The gate of nMOS transistor 604 iscoupled to the input “in” and to the gate of pMOS transistor 602.

The source of pMOS transistor 606 is coupled to a high voltage source“V”. The drain of pMOS transistor 606 is coupled to the source of pMOStransistor 602 and to the source of pMOS transistor 610. The gate ofpMOS transistor 606 is coupled to the second terminal of resistor 614and to the gate of nMOS transistor 608.

The source of nMOS transistor 608 is coupled to a low voltage and/orgrounded voltage. The drain of nMOS transistor 608 is coupled to thesource of nMOS transistor 604 and to the source of nMOS transistor 612.The gate of nMOS transistor 608 is coupled to the second terminal ofresistor 614 and to the gate of pMOS transistor 606.

The source of pMOS transistor 610 is coupled to the drain of pMOStransistor 606 and to the source of pMOS transistor 602. The drain ofpMOS transistor 610 is coupled to the output “out” and to the drain ofnMOS transistor 612. The gate of pMOS transistor 610 is coupled to theinverse input “!in” and to the gate of nMOS transistor 612.

The source of nMOS transistor 612 is coupled to the source of nMOStransistor 604 and to the drain of nMOS transistor 608. The drain ofnMOS transistor 612 is coupled to the drain of pMOS transistor 610 andto the output “out”. The gate of nMOS transistor 612 is coupled to theinverse input “!in” and to the gate of pMOS transistor 610.

The first terminal of resistor 614 is coupled to the drain of pMOStransistor 602 and to the drain of nMOS transistor 604. The secondterminal of resistor 614 is coupled to the gate of pMOS transistor 606and to the gate of nMOS transistor 608.

While FIG. 5 illustrates some embodiments using CMOS (ComplementaryMetal Oxide Semiconductor) implementations it is understood that otherembodiments may not use all MOS or CMOS technology, or any MOS or CMOStechnology.

In some embodiments the CMOS transistors of FIG. 6 may have a length of80 nm or of approximately 80 nm. In some embodiments widths of p-channeltransistors 602, 606 and 610 are 9.2 um or are approximately 9.2 um. Insome embodiments widths of n-channel transistors 604, 608 and 612 and528 are 4 um or are approximately 4 um. In some embodiments a resistanceof resistors 614 is 5000 ohms or is approximately 5000 ohms. In someembodiments high voltage value for the provided high voltage at thesource of transistor 606 is 1.2 volts or is approximately 1.2 volts. Insome embodiments the provided low voltage at the source of transistor608 is 0 volts or is approximately 0 volts. Although exemplary valuesfor transistor lengths, transistor widths, resistances and providedvoltages are provided above, other values for some or all of theseelements may be used according to some embodiments.

FIG. 7 illustrates a Bazes amplifier 700 that may be used inimplementing some embodiments. Amplifier 700 includes an input “in”, aninverse input “!in”, a bias voltage input Vb1, a bias voltage input Vb2,an output “out”, a pMOS transistor 702, an nMOS transistor 704, a pMOStransistor 706, and nMOS transistor 708, a pMOS transistor 710 and annMOS transistor 712. Voltages Vb1 and Vb2 are bias voltages provided atthe gates of pMOS transistor 706 and nMOS transistor 708, respectively.The bias voltages Vb1 and Vb2 set the current for two current sources. ABazes amplifier such as amplifier 700 may be used in implementing someembodiments.

Each of the transistors 702, 704, 706, 708, 710 and 712 includes asource, a drain and a gate. The source of pMOS transistor 702 is coupledto the drain of pMOS transistor 706 and to the source of pMOS transistor710. The drain of pMOS transistor 702 is coupled to the drain of nMOStransistor 704. The gate of pMOS transistor 702 is coupled to the input“in” and to the gate of nMOS transistor 704. The source of nMOStransistor 704 is coupled to the drain of nMOS transistor 708 and to thesource of nMOS transistor 712. The source of pMOS transistor 706 iscoupled to a high voltage source “V”. The gate of pMOS transistor 706 iscoupled to the bias voltage Vb1. The source of nMOS transistor 708 iscoupled to a low voltage source (and/or ground voltage). The gate ofnMOS transistor 708 is coupled to the bias voltage Vb2. The drain ofpMOS transistor 710 is coupled to the output “out” and to the drain ofnMOS transistor 712. The gate of pMOS transistor 710 is coupled to theinverse input “!in” and to the gate of nMOS transistor 712.

FIG. 8 illustrates a Chappell amplifier 800 that may be used inimplementing some embodiments. Amplifier 800 includes an input “in”, aninverse input “!in”, an output “out”, a pMOS transistor 802, an nMOStransistor 804, a pMOS transistor 806, a pMOS transistor 810 and an nMOStransistor 812. A Chappell amplifier such as amplifier 800 may be usedin implementing some embodiments.

Each of the transistors 802, 804, 806, 810 and 812 includes a source, adrain and a gate. The source of pMOS transistor 702 is coupled to thedrain of pMOS transistor 806 and to the source of pMOS transistor 810.The drain of pMOS transistor 802 is coupled to the drain of nMOStransistor 804, the gate of nMOS transistor 804, the gate of nMOStransistor 812, and to the gate of pMOS transistor 806. The gate of pMOStransistor 802 is coupled to the input “in”. The source of nMOStransistor 804 is coupled to a low voltage source (and/or groundvoltage). The source of pMOS transistor 806 is coupled to a high voltagesource “V”. The drain of pMOS transistor 810 is coupled to the output“out” and to the drain of nMOS transistor 812. The gate of pMOStransistor 810 is coupled to the inverse input “!in”. The source of nMOStransistor 812 is coupled to a low voltage source (and/or groundvoltage) which may be the same voltage as coupled to the source of nMOStransistor 804.

FIG. 9 illustrates an apparatus 900 according to some embodiments. Insome embodiments apparatus 900 is a p-channel implementation. Apparatus900 includes an input “in”, an inverse input “!in, an output “out”, apMOS transistor 902, a pMOS transistor 904, a pMOS transistor 906, apMOS transistor 908, an nMOS transistor 910, an nMOS transistor 912, annMOS transistor 914, an nMOS transistor 916, a pMOS transistor 822, annMOS transistor 924, a pMOS transistor 926, a pMOS transistor 928, annMOS transistor 930, a pMOS transistor 932, an nMOS transistor 934, apMOS transistor 936, a pMOS transistor 938 and an nMOS transistor 940.

In some embodiments pMOS transistors 902, 904, 906, 908 and nMOStransistors 910, 912, 914 and 916 form an amplifier. In some embodimentspMOS transistors 922, 926 and 928 and nMOS transistors 924 and 930 forma first inverter. In some embodiments pMOS transistors 932, 936 and 938and nMOS transistors 934 and 940 form a second inverter. The amplifiers,first inverter and second inverter mentioned above in reference to FIG.9 may be implemented in various embodiments illustrated and/or describedherein and in other embodiments.

FIG. 10 illustrates a system 1000 according to some embodiments. System1000 includes a transmitter 1002, a receiver 1004 and a transmissionline 1006 coupled between the transmitter 1002 and the receiver 1004.Receiver 1004 includes an amplifier 1012, a delay and gain circuit 1014and feedback 1016 from an output of the delay and gain circuit to theamplifier 1012. In some embodiments the closed loop gain of theamplifier 1012 never exceeds its open loop gain. Varying the delay andgain of the delay and gain circuit 1014 selects the frequency at whichmaximum amplifier gain is achieved. In some embodiments the amplifier1012 may be any type of amplifier including the amplifiers illustratedand described herein. In some embodiments the delay and gain circuit1014 may be any type of delay and gain circuit including the delay andgain circuits (and/or two inverter circuits) illustrated and describedherein. In some embodiments the gain/bandwidth of the apparatusincluding amplifier 1012 and delay and gain circuit 1014 is the samemagnitude as the loss/bandwidth of the transmission line 1006.

Any of the amplifiers illustrated and described herein (for example,amplifier 102 in FIG. 1, amplifier 202 in FIG. 2, and/or amplifier 1012in FIG. 10) could be a variety of different amplifiers in someembodiments, including but not limited to a Bazes amplifier similar toor the same as the Bazes amplifier illustrated in FIG. 7, a Chappellamplifier similar to or the same as the Chappell amplifier illustratedin FIG 8, a hybrid amplifier such as the amplifier illustrated in FIG. 5and/or in FIG. 6, an amplifier such as the amplifier in FIG. 9, or anyother amplifier.

In some embodiments the techniques and circuits described herein areimplemented within a high speed serial receiver or transceiver. Damageadded by a transmission line may be repaired using some embodiments.Some embodiments may be implemented in receivers or in transceivers.Some embodiments may be implemented in any circuit including anamplifier. Some embodiments may be implemented in any receiver, anytransceiver and/or any clock tree that distributes clock pulses tovarious devices in a chip or a system.

In each system shown in a figure, the elements in some cases may eachhave a same reference number or a different reference number to suggestthat the elements represented could be different and/or similar.However, an element may be flexible enough to have differentimplementations and work with some or all of the systems shown ordescribed herein. The various elements shown in the figures may be thesame or different. Which one is referred to as a first element and whichis called a second element is arbitrary.

An embodiment is an implementation or example of the inventions.Reference in the specification to “an embodiment,” “one embodiment,”“some embodiments,” or “other embodiments” means that a particularfeature, structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the inventions. The various appearances“an embodiment,” “one embodiment,” or “some embodiments” are notnecessarily all referring to the same embodiments.

If the specification states a component, feature, structure, orcharacteristic “may”, “might”, “can” or “could” be included, forexample, that particular component, feature, structure, orcharacteristic is not required to be included. If the specification orclaim refers to “a” or “an” element, that does not mean there is onlyone of the element. If the specification or claims refer to “anadditional” element, that does not preclude there being more than one ofthe additional element.

The inventions are not restricted to the particular details listedherein. Indeed, those skilled in the art having the benefit of thisdisclosure will appreciate that many other variations from the foregoingdescription and drawings may be made within the scope of the presentinventions. Accordingly, it is the following claims including anyamendments thereto that define the scope of the inventions.

1. An apparatus comprising: an amplifier; and a delay and gain circuitcoupled to an output of the amplifier, wherein an output of the delayand gain circuit is fed back to the amplifier; wherein the amplifierprovides positive feedback and the output of the delay and gain circuitis fed back to the amplifier as negative feedback; and wherein theamplifier mixes the positive feedback and the negative feedback.
 2. Theapparatus as claimed in claim 1, wherein the amplifier is a CMOSamplifier.
 3. The apparatus as claimed in claim 2, wherein the CMOSamplifier is a hybrid Bazes and Chappell amplifier.
 4. The apparatus asclaimed in claim 3, wherein: the amplifier includes a first, a secondand a third pMOS transistor and a first, a second and a third nMOStransistor; a gate of the first pMOS transistor and a gate of the firstnMOS transistor are coupled to an input; a gate of the second pMOStransistor and a gate of the second nMOS transistor are coupled to adrain of the first pMOS transistor and a drain of the first nMOStransistor; and a gate of the third pMOS transistor and a gate of thethird nMOS transistor are coupled to an inverse input.
 5. The apparatusas claimed in claim 4, wherein the gate of the second pMOS transistorand the gate of the second nMOS transistor are coupled to the drain ofthe first pMOS transistor and the drain of the first nMOS transistor viaa resistor.
 6. The apparatus as claimed in claim 1, wherein the delayand gain circuit includes a first inverter and a second inverter.
 7. Theapparatus as claimed in claim 6, wherein the second inverter isapproximately four times the size of the first inverter.
 8. Theapparatus as claimed in claim 6, wherein the first inverter isapproximately one-fourth the size of the output of the amplifier.
 9. Theapparatus as claimed in claim 6, wherein the first inverter isapproximately one-fourth the size of the output of the amplifier and thefirst inverter is approximately one-fourth the size of the secondinverter.
 10. The apparatus as claimed in claim 1, wherein the amplifierfurther includes a resistor.
 11. The apparatus as claimed in claim 6,wherein the amplifier further includes a resistor.
 12. The apparatus asclaimed in claim 1, wherein the amplifier further includes a resistorthat mixes the positive feedback and the negative feedback.
 13. Theapparatus as claimed in claim 6, wherein the amplifier further includesa resistor that mixes the positive feedback and the negative feedback14. The apparatus as claimed in claim 4, wherein the amplifier furtherincludes a resistor, wherein the resistor is included in a circuit thatmixes positive feedback provided by the amplifier and negative feedbackprovided to the amplifier from the output of the second inverter. 15.The apparatus as claimed in claim 6, wherein the amplifier furtherincludes a resistor, wherein the resistor is included in a circuit thatmixes positive feedback provided by the amplifier and negative feedbackprovided to the amplifier from the output of the second inverter. 16.The apparatus as claimed in claim 1, further comprising an output,wherein the output is coupled to the output of the second inverter. 17.The apparatus as claimed in claim 16, wherein the output does notinclude evidence of precharging from the amplifier.
 18. The apparatus asclaimed in claim 6, further comprising an output, wherein the output iscoupled to the output of the second inverter.
 19. The apparatus asclaimed in claim 18, wherein the output does not include evidence ofprecharging from the amplifier.
 20. The apparatus as claimed in claim 1,wherein the amplifier includes a resistor, and wherein the resistor isincluded in a circuit that mixes the positive feedback and the negativefeedback.
 21. The apparatus as claimed in claim 1, the amplifier furthercomprising: an inverse input; a first pMOS transistor having a gatecoupled to the input of the amplifier; a second pMOS transistor; a thirdpMOS transistor having a gate coupled to the inverse input of theamplifier and having a source coupled to a source of the first pMOStransistor and to a drain of the second pMOS transistor; a first nMOStransistor having a gate coupled to the input of the amplifier; a secondnMOS transistor having a gate coupled to a drain of the first pMOStransistor, a drain of the first nMOS transistor, and to a gate of thesecond pMOS transistor; and a third nMOS transistor having a gatecoupled to the inverse input of the amplifier, a drain coupled to adrain of the third pMOS transistor and a source coupled to a source ofthe first nMOS transistor and to a drain of the second nMOS transistor,wherein the output of the amplifier is coupled to the drain of the thirdpMOS transistor and to the drain of the third nMOS transistor.
 22. Theapparatus as claimed in claim 21, the amplifier further comprising aresistor, wherein the gate of the second nMOS transistor and the gate ofthe second pMOS transistor are coupled directly together, and the drainof the first pMOS transistor and the drain of the first nMOS transistorare coupled directly together, wherein the direct coupling of the gateof the second nMOS transistor and the gate of the second pMOS transistorare coupled via the resistor to the direct coupling of the drain of thefirst pMOS transistor and the drain of the first nMOS transistor. 23.The apparatus according to claim 22, wherein the resistor has aresistance of approximately 5000 ohms.
 24. The apparatus according toclaim 21, the amplifier further comprising a control input, wherein thegate of the second nMOS transistor and the gate of the second pMOStransistor are coupled to the control input.
 25. The apparatus accordingto claim 21, wherein a width of each of the first pMOS transistor, thesecond pMOS transistor and the third pMOS transistor is approximately9.2 um, and wherein a width of the first nMOS transistor, the secondnMOS transistor and the third nMOS transistor is approximately 4 um. 26.The apparatus according to claim 25, wherein a length of each of thefirst pMOS transistor, the second pMOS transistor, the third pMOStransistor, the first nMOS transistor, the second nMOS transistor andthe third nMOS transistor is approximately 80 nm.